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    Performance Based Design

    rstroup27 Oct 4 '11 0

    Currently, I've been in three courses which have assisted my year-long independent research project: a new method for designing reinforced concrete shear walls.  The project is to be designed for the Pankow Foundation, an organization out of Claremont, CA, founded on the vision to improve construction methods through research.

    Typical concrete shear wall design is not an easy task.  In the past, most walls have been designed so as to be a combination of column and wall, utilizing what most architects like to refer as pilasters, which extrude at the ends from the interior of the flat wall.  A good example of what that would typically look like is shown below.

    For our design, we're introducing past standards to current performance-based criteria.  By looking at what has worked in the past vs. what is required by seismic design, it is our belief that just building a shear wall straight upon a fixed condition isn't suitable anymore.  (By fixed, I mean any structural assembly which transfers axial, shear and moment force into the ground).

    Why is this?  Because Load and Resistance Factor Design (LRFD for short), which is incorporated across the steel and concrete design manuals for current construction, doesn't take into account deflection outside of the typical allowable deflection criterion (span/360 for live loads, span/240 for total loads).  If one looks closer - by say, using Abaqus or any other mechanical software that can compute individual stresses where member force transitions into reaction force - they can see residual stresses (not unlike those in steel) which build up toward the base of the column/beam/member.  

    Those residual stresses are powerful.  Alone, they can permanently deform a structural member if that member reaches a load beyond it's yield.  By attempting to minimize that deflection, one could minimize damage in heavily seismic areas, and for this reason alone, a new shear wall system should be devised.

    One of the techniques is by eliminating the fixed condition and replacing it with a new form of pinned connection - one that effectively evolves the structural system from a "lincoln log" mechanical assemblage to that of a "guitar string."  Essentially, we're attempting to make the building more ductile, and this is our crazy idea.  In my next post, I will expound on this idea and show the solutions we are currently employing to understand reinforced concrete shear walls a little more thoroughly.  

     

     
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About this Blog

I'm currently earning my masters in structural engineering at Lehigh University, but I hold a bachelors of architecture from the University of Oregon. What I would like to write about has to do with my aforementioned diverse background, i.e., what lessons I've learned in structural engineering that may help me as an architect in the near future.

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